1. Field of the Invention
The invention relates to curable organopolysiloxane compositions, to methods for the production thereof, and to the use thereof, in particular in the production of artificial stone.
2. Description of the Related Art
Artificial stone consisting of from 5 to 80% by weight organic polymer resins crosslinkable with suitable catalysts and from 20 to 95% by weight fillers, such as, for example, substances comprising silicon dioxide (quartz, quartzite, granite, porphyry, sand, silicates, clays, etc.), substances comprising calcium carbonate (marble, limestone, dolomite, etc.), substances comprising calcium or barium sulfate, aluminum oxide, aluminum trihydrate, magnesium oxide, magnesium hydroxide, zinc oxide and silicon carbide have been known for a long time. Reference is made in this connection, for example, to U.S. Pat. No. 4,643,921, including the literature cited therein, which is to form part of the disclosure of the present invention.
The polymer resin base used thereby, for example in Bretonstone® or Silestone® technology, is a radically crosslinkable polyester resin in combination with a reactive solvent such as styrene or methyl methacrylate or mixtures thereof. Reference is made in this connection, for example, to US-A 2008/0296795, including the literature cited therein, which is to form part of the disclosure of the present invention.
Furthermore, there are artificial stones which, instead of polyester resins, comprise methacrylate resins, as described in US-A 2011/0207849, wherein the specifications mentioned as prior art in that publication are likewise to form part of the disclosure of the present invention relative to the organic polymer resin binders based on polyester resin or methacrylate resins described therein.
There are further described as the resin base, for example in US-A 2009/0253829, epoxidized triglycerides from natural sources in the presence of cyclic, alkyl-substituted carboxylic anhydrides, Melamine resins, however, are also used as a polymer resin base in artificial stone, in U.S. Pat. No. 3,670,060.
A disadvantage of all the compositions known hitherto is that the binders have only limited resistance to UV radiation and weathering. This is outwardly visible because, in particular in the case of dark color shades, the colors of the artificial stone becomes significantly lighter and, in addition, they lose their sheen. In addition, the polymer matrix is not stable to heat, that is to say the polymers depolymerize with pronounced discoloration. Moreover, the cured organic polymer matrix, despite high filler contents, is flammable and sometimes burns with a very sooty flame.
Filled compositions based on organosiloxanes are likewise described in the literature. DD-A 103 252, for example, claims a method for producing molding compositions based on linear organopolysiloxanes. DE-A 2 504 357 describes silicone resin molding compositions, the crosslinkable resin base of which is composed of organopolysiloxane having at least 1.0% by weight Si-bonded OH groups and a linear diorganopolysiloxane having OH or triorganosilyl end groups. In U.S. Pat. No. 3,108,985, phenyl-alkylsiloxanes are claimed as the resin base. It is a disadvantage in all these cases, that despite high curing temperatures, only comparatively low hardnesses of the test specimens are achieved. In addition, harmful lead compounds are used as catalyst.